In craniotomies, access to the cranium is typically achieved by the creation of a hole in the skull. This hole or window is usually created by identifying the area of the brain to which access is needed, drilling several burr holes into the skull near the periphery of this area, inserting a cutting tool into one of the burr holes, and making cuts from one burr hole to another, i.e., connecting osteotomies. Removing the cut-out area of the skull, i.e. the bone flap, provides the desired access to the cranium.
If all of the burr holes are joined by cuts such that the cuts form a complete outline of the window, then the bone flap can simply be removed. Alternatively, if the cuts form only a partial outline of the window, then the bone flap can be bent out of the way. Although the size and shape of the bone flap will vary with the desired cranial access area and size, a typical flap would be generally rectangular in shape and approximately four by six centimeters.
After the desired medical or surgical procedure on the cranium has been performed, the bone flap must be replaced and held in a stable position to allow the skull to heal. Known methods of fixing the bone flap to the skull include drilling pairs of threading holes in the edges of the skull and bone flap, threading wire through the holes, and twisting or tying the ends of the wire together to secure the edges. Disadvantages of this method include the tedious nature and length of time required for the procedure and the possibility of injury to the dura by drilling the threading holes too deep or by the sharp ends of the wires.
Another method of fixation involves the use of bone plates which are secured across the connecting osteotomies by screws. The disadvantages associated with the use of plates and screws relate to the undesirable cosmetic appearance resulting from the protrusion of the plate and screw above the bone surface. As there is minimal intervening soft tissue between the skull and the skin, unappealing external appearance is particularly a problem. The lack of soft tissue also has the unwanted consequence of permitting the patient to feel the plate and screw simply by pressing on the scalp. Thus, there is a need for improved devices for fixing a bone flap to a skull.